What happens during the intake and compression strokes of four stroke engines?

on the intake stoke, the piston is going down to the bottom of the cylinder. As it is going down the intake valve opens and allows a mixture of air and gas in the chamber.

the piston ,once it reaches the bottom of the cylinder,it starts to travel upward(this is the start of the compression stroke) and compresses the air/fuel mixture,and at the same time the intake velve closes,craeting a sealed chamber. As the piston continues to go up it keeps squeezing the air and fuel and just before it tops out the spark-plug fires,igniting this mixture which drives the piston down,starting the power stroke.

Power and Intake (novanet)